# year    value 
 1980 5.247693 
 1981 5.507627 
 1982 5.299562 
 1983 5.038669 
 1984 3.700683 
 1985 4.473458 
 1986 5.110865 
 1987 5.933262 
 1988 5.608289 
 1989 5.488042 
 1990 5.909656 
 1991 5.396225 
 1992 5.461064 
 1993  5.84392 
 1994 5.121029 
 1995  5.46196 
 1996 4.876616 
 1997 5.662981 
 1998  5.48146 
 1999 6.840507 
 2000 5.428265 
 2001 5.925364 
 2002  6.68858 
 2003 5.606913 
 2004 6.339214 
 2005 4.913199 
 2006 5.752168 
 2007 6.668589 
 2008 4.055066 
 2009 6.740086 
 2010 5.647624 
 2011 4.958683 
 2012 3.869931 
 2013 5.189295 
 2014 5.240479 
 2015 6.215868 
 2016 6.327662 
 2017 6.760105 
 2018 5.620899